Angel #1.8: I Will Remember You
Wiki says that this episode is usually rated as the Best Angel Episode Ever. Hard to imagine it being topped, but I assume this is because it ends the Buffy/Angel love story? It did feel like a Buffy episode, in some sense. She shows up in LA, which leads to a demon attack, which leads to Angel becoming alive, which leads to their love returning, which leads to Angel worrying about her safety, which leads to him sacrificing his new life and becoming a vampire again, which leads to Buffy’s memory being erased, which leads to Angel forever carrying the burden of the happiness of the one day together. It was sad and weepy and mostly everything Buffy-verse stories are.